Recently, semiconductor devices have come to include a plurality of power circuits on a chip. The power circuits respectively drive a variety of circuits, for example, a constant voltage circuit, a motor drive circuit, an illumination control circuit, and so on. The semiconductor device also includes power transistors which may generate heat due to a large current flow through the power transistor. A current limit circuit is generally used to reduce such heat generation by cutting off the current flow.
However, a temperature of the semiconductor device is also affected by an ambient temperature and a power consumption of the semiconductor device. When the ambient temperature is low or a voltage applied to the power transistor is low, more current than a current value being limited by the current limiter circuit may be allowed to flow with no problem. Conversely, when the ambient temperature is high, the temperature of the semiconductor device may easily exceed an acceptable maximum value before the current limit circuit starts to limit the current.
Thus, it is insufficient to protect the semiconductor device from overheating using only the current limiter circuit. Therefore, temperature sensing elements may be employed and provided near heat generating elements such as the power transistors in the semiconductor device. When the temperature sensing element detects a high temperature exceeding a predetermined temperature, the semiconductor device limits current flow through the power transistor to avoid overheating problem.
Recently, as electrical devices have become more advanced, more functions are provided with the electrical devices. For this reason, one chip semiconductor device that is an example of such electrical devices generally includes a plurality of power circuits on a chip. The electrical device needs to control power to the circuits by selectively switching the power circuits on/off such that power is not supplied to circuits that do not contribute a function. Furthermore, power is supplied to those circuits that contribute functions and power is always supplied to a control circuit that controls the whole system of the electrical device. Thus, controlling the power circuits in the electrical device has become more and more complicated.
In a conventional electrical device, a temperature sensor may be provided at each power circuit and the power supply circuit is stopped when the temperature of the power supply circuit increases and exceeds a predetermined value. Further, an importance rank table that describes conditions for power supply circuits at various cases may be prepared, such that, when the temperature sensor detects an abnormal temperature at one power circuit, the electrical device may output a plurality of power control signals based on the importance rank table to manage the whole system of the electrical device.
However, in the conventional electrical device, a large number of comparators equal in number to the number of temperature sensors, are needed to compare each output value of the temperature sensor with a reference voltage. As the number of the temperature sensors increases, a circuit size of the electrical device increases. Further, the circuit looses flexibility, when the circuit is adapted for a specific use by configuring so as to output a plurality of the power control signals based on the predetermined importance rank table.